(1) Field of the Invention
The invention relates to a method of fabricating a photoresist mask, and more particularly, to a method of fabricating a bi-layer photoresist mask that will improve critical dimension control in the manufacture of integrated circuits.
(2) Description of the Prior Art
Device sizes continue to shrink as semiconductor manufacturing processes are improved. Continuing advancement in the production of ever smaller devices is limited by photolithography techniques. Dry development processes, such as silylation, can increase the overall process window for micro-patterning techniques. Dry development processes can improve resolution and depth of focus and result in more vertical resist profiles. However, proximity effect and thinning effects exist which make post-silylation critical dimension control challenging. Proximity effect refers to the phenomenon in which a pattern element adjacent to another pattern element receives light exposure not only from the incident light waves, but also from light waves reflected from the adjacent element. As pattern elements become closer together, the proximity effect is more pronounced. Thinning effects occur when a thin layer of photoresist is used. In certain areas, all of the photoresist may be etched away exposing areas of the underlying layer which should not be exposed. The edge profile of the silylated region determines the post dry-development critical dimension control. A vertical profile, achievable with dry etching, improves critical dimension control.
U.S. Pat. No. 5,455,145 to Tarumoto discloses a double layer resist mask. U.S. Pat. No. 4,657,629 to Bigelow teaches a double layered resist mask in which the first layer of resist is baked and entirely exposed to ultraviolet light. U.S. Pat. No. 5,427,649 to Kim et al teaches a double layer of resist film in which a portion of the first resist film is silylated before the second layer resist is formed. U.S. Pat. No. 5,525,192 to Lee et al disclose a process in which silylation and an alkali surface treatment of the resist are performed in parallel.